1. Field of the Invention
This invention relates to a mounting structure of a multiple piston ring for various internal combustion engines such as particularly a two cycle engine.
2. Description of the Prior Art
A conventional dual piston ring was invented in the 1930's. Such a dual piston ring had been used for the purpose of e.g. discharging any oil dust irrespective of its airtight maintenance, but nowadays, is rarely used. Any piston ring for packing purpose is disposed in a cylindrical groove formed upon an outer surface of a piston.
The profile of a gap in such a piston ring is various: namely, (1) a right-angled type gap (e.g. shown in FIG. 1 or FIG. 7), (2) an inclined type gap, (3) a step type gap, (4) a two-step type gap, etc. The gas leakage in such piston ring is mostly caused through the gap. When adjacent piston rings have respective step on their opposing side wall, the gas leakage is very little, but its machining process is expensive, and danger of fracture of the piston ring is probable. Accordingly, this type is scarcely used.
The right-angled type gap and the inclined type gap can be formed by a simple machining work, and are very popular. Yet, the quantity of the gas leakage is much due to such a gap.
To cope with this defect, it has been considered to form the piston ring groove in a multi-stage manner, due to which a labyrinth effect is obtained. However, since the gap is not sealed completely, it is not a final resolution.
Referring to FIGS. 1 and 2, a gas G is leaked from a gap Ex between adjacent side walls of a piston ring PR, so that a preferred packing effect cannot be attained. It brings a decline of an engine output and a discharge of an exhaust gas.
The springiness of the piston ring is generally weak, namely about 1 to 2 kg/cm.sup.2, while the combustion gas pressure of the gasoline engine is 35 kg/cm.sup.2 and that of the diesel engine is 60 kg/cm.sup.2.
Under such circumstances, the piston ring cannot resist such a high pressure gas. However, it maintains a weak fitting condition for a cylinder due to its weak springiness, thereby a unique packing effect is attained. More specifically when such a high pressure gas is applied to the piston ring, it is penetrated into a back side of the piston ring through a gap of about 0.05 mm, thereby the back side of it is pressurized and a high packing effect is attained.
The piston ring which is used today is provided with a gap of 0.5 to 1.00 mm in width. For this reason, the high pressure gas is freely passing through the gap, so that a sufficient packing effect is not obtained. Further, when the outer circumference of the piston ring is worn out, the gap of the piston ring is enlarged, so that the packing effect is reduced.
In view of the above, this invention has been accomplished.